Fixed #16481 -- Adapted one raw SQL query in cull immplementation of …

…the database-based cache backend so it works with Oracle. Thanks Aymeric Augustin for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16635 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache/backends/db.py

@@ -135,7 +135,13 @@ def _cull(self, db, cursor, now):
             cursor.execute("SELECT COUNT(*) FROM %s" % table)
             num = cursor.fetchone()[0]
             if num > self._max_entries:
-                cursor.execute("SELECT cache_key FROM %s ORDER BY cache_key LIMIT 1 OFFSET %%s" % table, [num / self._cull_frequency])
+                cull_num = num / self._cull_frequency
+                if connections[db].vendor == 'oracle':
+                    # Special case for Oracle because it doesn't support LIMIT + OFFSET
+                    cursor.execute("SELECT cache_key FROM (SELECT ROW_NUMBER() OVER (ORDER BY cache_key) AS counter, cache_key FROM %s) WHERE counter > %%s AND COUNTER <= %%s" % table, [cull_num, cull_num + 1])
+		else:
+                    # This isn't standard SQL, it's likely to break with some non officially supported databases             
+                    cursor.execute("SELECT cache_key FROM %s ORDER BY cache_key LIMIT 1 OFFSET %%s" % table, [cull_num])
                 cursor.execute("DELETE FROM %s WHERE cache_key < %%s" % table, [cursor.fetchone()[0]])
 
     def clear(self):